PH RO/DI water too low

[wanecek]

Hi there,

Well, I found out why my aquarium water has had low PH. I went and got a PH monitor and measured the water from my RO/DI and it comes out at 7.4. Is this normal?

I went out yesterday and got some buffer and got my PH back up to 8.15. So with the low PH coming out of my RO/DI will I have to use buffer going forward or can I do something to the RO/DI water before it is put into the sump? Stupid question but I rather not have to add buffer in every 2 weeks. This will just add to the already expensive hobby of reefing and leave less money for corals and fish.

Thanks,

Michael

[faviasteve]

Pure water, which is what the RO/DI process is supposed to produce, should have a PH of about 7.0. This is normal. I've heard it can be more acidic than that becuase of dissolved carbon dioxide. It has a PH of about 7.0 because it has equal numbers of H+(aka H30+) and OH- ions. Carbonate/bicaronate aka buffer aka alkallinity bonds with or releases H+ ions so the PH is approximatey 8.3. Adding un-buffered top-off water to your aquarium is safe. It won't mess up the PH.
Aquarium water becomes more acidic over time because of organic acids released from various biological processes, not from adding RO/DI water.

Steve

[Boomer]

RO/DI and it comes out at 7.4. Is this normal?

Basically, it is useless, to try and measure the pH of RO/DI water, as there is nothing in the water for the pH kit or meter to respond to. The water needs other ions, other than just H+/H3O or OH-. The pH can be just about anywhere via so called testing. Randy's RO/DI water, for example, has a pH of 9. Others have had it in the 6's according to the test they took.

[wanecek]

Thanks to the both of you for explaining how RO/DI water affects the aquarium water. I guess I am back to trying to figure out what is causing my decrease in PH, especially since I only have xenia, calupera and chaeto in my aquarium.

Thanks,
Michael

[Randy Holmes-Farley]

I agree that it is pointless to measure the pH of RO/DI water, and regardless of what you measure, it is not typically a contributor to low tank pH.

Pure water has a pH of about 7, but as it interacts with air, the pH drops into the 6's or even lower. My Ro/DI water measures pH 9+ ! I'm not sure if that is real or not.

Low pH is caused by excess CO2 in the tank and/or home air. This article should help you diagnose and solve the problem:

Low pH: Causes and Cures
http://reefkeeping.com/issues/2004-09/rhf/index.htm